Method of melting and casting magnesium and alloys rich in magnesium



Patented Aug. 16, 1938 METHOD OF MIELTING AND CASTING MAG- NESIUM AND ALLO SIUM YS RICH IN MAGNE- Leopold Lasch and Georg Schichtel, Radenthein,

Austria,

assignors to American Magnesium Metals Corporation, Pittsburgh, Pa., a corporation of Delaware No Drawing; Application September 16, 1936,

Serial No. 101,083. In

Austria October 7,

'3 Claims. (Cl. 75-67) The invention relates to a method of melting magnesium and its alloys and handling such material in a molten condition.

The main object of the invention is to provide a simple and commercially practicable process for protecting the magnesium and its alloys against the action of air during the melting and the subsequent handling of the molten batch of metal, without contaminating the melt with foreign body.

Another object is to provide a method of the above indicated character whereby magnesium and its alloysmay be melted without taking up even traces of impurities which would give rise to corrosion of the compact metal resulting from the melt.

In melting down magnesium or alloys rich in magnesium in the presence of air, the magnesium catches fire unavoidably during the melting process, with the formation of oxides and nitrides. The consequence is not only an appreciable loss of metal but also the danger that, on the pouring of the metal burning in the crucible, portions of the oxides and nitrides formed on the surface of the melt find their way. into the casting, with the result that the mechanical properties of the casting are deleteriously affected.

Hitherto this drawback has been combatted by either applying mixtures of salts to the surface of the melt, which salts are fused at the working temperature, or working in tightly closed crucibles with the exclusion of air, with the view of preventing the action of the air upon the material. requires the use of means which are not available to the majority of foundries it has been as a rule necessary to have recourse to covering over the surface of the metallic material by the use of fused salt mixtures. Nowthese salt mix--.

tures consist mainly of chlorides or containthe same in preponderating amounts. Now, small portions of the salt melt "oiteniindtheir'way .into the casting and these particles cause the formation of tubercular corrosions. This is the more troublesome since from these starting points the dreaded corrosion of the metal, by which the mechanical properties of the casting are appreciably deteriorated, spreads further over the surface. When melting down and casting metallic material which is free from chlorine from the outset it is a still greater disadvantage if this metal takes up even traces of chlorides as a. consequence of the employment of a salt coating containing chlorine.

The present invention obviates this drawback Since the second of these expedients' by applying to the melting or molten metallic material practically anhydrous solid organic substances which burn with the formation of a froth inert to magnesium, and which yield, on carbonizatlon, a hard crust of a nature not to become wetted by molten magnesium. This behavior leads to the final result that a protective covering becomes formed over the entire surface of the melt. These substances protect the molten metal from the action of the air'first by means of the evolved combustion gases, then by the formation of froth, and finally by means of the resulting solid crust which does not become wetted by the liquid metal beneath it. Substances particularly well suited for this purpose are the following: Asphalt, casein, horn meal, and sugar, which may be used individually or in various mixtures. The substances used are strewn in the form of powder upon the melt, whereupon the process outlined above proceeds, up to the formation of the solid protective crust, in the course of a few seconds. It is advisable to increase the specific gravity of these substances by the addition of inorganic chlorine-free compounds of higher specific gravity, which have no deleterious effect upon the molten metal, examples being fluorspar and dead burned magnesite.

Before pouring, the coating is detached from the rim of the crucible and the metal poured from beneath the coating. The coating floats on the metal without crumbling. When the starting material used is free from chlorine there are obtained in this manner castings or ingots which are entirely free from chlorine, that is to say industrial material with which there is no danger whatever of corrosion resulting from local chloride inclusions. At the same time losses by burning are reduced to a minimum, since burning of the melt cannot occur.

In practlsingthe method, for example, a mixtl118 of one part. by weight of pulverulent horn meal and two parts by weight of fiuorspar is strewn upon the smooth surface of the metal after the latter has been refined in the usual manner. Of this mixture a quantity amounting to about 2% of the weight of the metal is suflicient to form a coating which is completely impervious to air when using the usual crucibles.

The term "horn meal means, as customarily, a nitrogenous manure, obtained from hoofs, horns, and claws, by treating them with superheated steam, drying, and grinding.

What we claim is: 1. A method of preventing the action of air upon molten magnesium and magnesium alloys, 58

which comprises applying to the metallic material practically anhydrous solid organic substance capablcof combusting in theair, at the working temperature, with the formation of a froth inert to magnesium, and allowing such a froth to be formed in contact with the'heated metal, which froth becomes then converted, by carbonization, into a hard crust covering the freely exposed surface of the melt.

2. A method of preventing the action of air upon molten magnesium and magnesium alloys, which comprises bringing asphaltic material in contact with the heated metal under treatment to first produce a froth and then, by carbonization of the froth formed, a hard protective crust over the free surface of the molten metal.

3. A method of preventing the actionofairupon molten magnesium and magnesium alloys, which comprises bringing casein in contact with the heated metal under treatment to first produce a froth and then, by carbonization of the froth formed, a hard protective crust over the free surface of the molten metal.

4. A method of preventing the action of air upon molten magnesium and magnesium alloys,

-which comprises bringing sugar in contact with the heated metal under treatment to first produce a froth and then, by carbonization of the froth formed, a hard protective crust over the free surface of the molten metal.

5. A method of melting magnesium and its alloys, consisting in applying to the melting material practically anhydrous solid organic substance capable of combusting in the air, at the working temperature, with the formation of a froth inert to magnesium, and allowing such a froth to be formed all over the free surface of the metal as the melting proceeds, which froth becomes then converted, by carbonization, into a hard crust covering the freely exposed surface of the melt.

6. A method of handling molten magnesium and its alloys, which comprises placing onto the surface of the molten metal practicall anhydrous solid organic substance capable of combusting in the air, at the working temperature, with the formation of a froth inert to magnesium, and allowing such a froth to be formed over the surface of the molten metal, which froth becomes then converted, by carbonization, into a hard crust covering the freely exposed surface of the melt.

7. A method of preventing the action of air upon molten magnesium and magnesium alloys, which comprises applying to the metallic material practically anhydrous solid organic substance capable of combusting in the air, at the working temperature, with the formation of a froth inert to magnesium, with an addition of a relatively smaller amount of an inorganic chlorine-free loading material non-volatile at the working temperature which has no deleterious effect upon the molten metal, and allowing such a froth to be formed in contact with the heated metal, which froth becomes then converted, by carbonization, into a hard crustcovering the freely exposed surface of the melt.

LEOPOLD LASCH. GEORG SCHICH I EL. 

